The endocytoscopy system is a novel diagnostic technique that provides extremely high-magnification imaging of the gastrointestinal mucosa. We are currently using a prototype Olympus endocytoscope for clinical research in gastrointestinal tumors. In one surgical specimen obtained after resection of a cancer of the transverse colon, focal abnormalities of colonic glands were detected 7 cm away from the primary tumor, within macroscopically normal mucosa. Our finding, which was confirmed by histopathological examination, suggests the need for further clinical investigation to assess whether endocytoscopy is able to identify premalignant changes in apparently normal mucosa. This could potentially be useful for accurate evaluation before planning minimally invasive therapy.